1. Field of the Invention
The present invention relates to a device for decoding Manchester encoded data and more particularly relates to technology for decoding Manchester encoded data to NRZ (Non Return Zero) encoded data.
2. Description of Related Art
In Manchester code, code of a rectangular wave pattern xe2x80x9c10xe2x80x9d is assigned to the binary number xe2x80x9c1xe2x80x9d and the rectangular waveform xe2x80x9c10xe2x80x9d takes the bit period of the binary number xe2x80x9c1xe2x80x9d as one period. Manchester code also assigns a rectangular waveform xe2x80x9c01xe2x80x9d to the binary number xe2x80x9c0xe2x80x9d, with the rectangular waveform for the binary number xe2x80x9c0xe2x80x9d having a phase difference of 180 degrees with respect to the rectangular waveform for the binary number xe2x80x9c1xe2x80x9d.
When binary data (NRZ encoded data) is decoded from Manchester encoded data, a decoding device detects information for one of the leading half or the following half of the bit period of the Manchester encoded data. If this information can be detected, the decoding device can decode whether the Manchester encoded data is a binary xe2x80x9c1xe2x80x9d or xe2x80x9c0xe2x80x9d.
Related devices regenerate a decoding clock from transition points of the Manchester encoded data and then synchronize the phase of the regenerated clock with the transition points of the Manchester encoded data. After the regenerated clock is synchronized, the related device generates a clock of a timing corresponding to one of the leading half or following half of the bit period of the Manchester encoded data. The related device then obtains decoded data by extracting information appearing at the timing of the generated clock.
For example, FIG. 2 shows a method for decoding Manchester encoded data employed in the related art.
FIG. 2 shows the flow of data when decoded data is obtained from the following half of the bit period for Manchester code transmitted by a related device at 1 Mbps.
FIG. 2(A) shows 1 Mbps NRZ data (xe2x80x9c1xe2x80x9d, xe2x80x9c0xe2x80x9d, xe2x80x9c1xe2x80x9d, xe2x80x9c1xe2x80x9d, xe2x80x9c0xe2x80x9d, xe2x80x9c0xe2x80x9d, xe2x80x9c1xe2x80x9d). FIG. 2(B) shows Manchester encoded data (xe2x80x9c10 xe2x80x9d, xe2x80x9c01xe2x80x9d, xe2x80x9c10xe2x80x9d, xe2x80x9c10xe2x80x9d, xe2x80x9c01xe2x80x9d, xe2x80x9c01xe2x80x9d, xe2x80x9c10 (where 0 is not shown in the drawings)xe2x80x9d). FIG. 2(C) shows regenerated clock data (12 clock portion). FIG. 2(D) shows decoded data 1 (xe2x80x9c1xe2x80x9d, xe2x80x9c1xe2x80x9d, xe2x80x9c0xe2x80x9d, xe2x80x9c0xe2x80x9d, xe2x80x9c1xe2x80x9d, xe2x80x9c1xe2x80x9d) obtained from data for the Manchester encoded data of FIG. 2(B) and data for the regenerated clock of FIG. 2(C). The phase of the decoded data 1 is xc2xe of a period behind when compared with the phase of the NRZ data of FIG. 2(A). FIG. 2(E) shows decoded data 2 (xe2x80x9c0xe2x80x9d, xe2x80x9c1xe2x80x9d, xe2x80x9c0xe2x80x9d, xe2x80x9c1xe2x80x9d, xe2x80x9c1xe2x80x9d, xe2x80x9c0xe2x80x9d, xe2x80x9c0xe2x80x9d) 180 degrees out of phase with the phase of the decoded data 1 of FIG. 2(D).
When decoded data is obtained, the related device phase synchronizes a regenerated clock having twice the frequency (2 MHz) of the Manchester encoded data with the Manchester encoded data. After the phase of the regenerated clock is synchronized with the transition points of the Manchester encoded data, the related device selects a clock timing corresponding to the following half of the bit period of the clock timings of two types of parity comprising the regenerated clock. The related device then samples the Manchester encoded data at the selected clock timing and takes the sampled data as decoded data.
FIG. 2(C) shows where a clock corresponding to the following half of the bit period is an even numbered clock. The related device then selects the even numbered clock as a sampling clock. FIG. 2(D) shows the results for the sampling clock. The results for the sampling clock are the decoded data 1. FIG. 2(E) shows the decoded data 1 with it""s polarity inverted. In reality, the related device obtains the polarity inverted data as the final decoded data 2.
Manchester code is characterized by values being of inverted polarities at the leading and following halves of the bit period. As a result of having this property, when the related device makes an erroneous sampling clock selection, the Manchester code is such that the polarity of the obtained decoded data is inverted.
In an actual circuit, it is necessary to separately provide a circuit for accurately discerning odd and even numbers of the regenerated clock.
When the Manchester encoded data is consecutive 1""s or 0""s the related device extracts the transition points for the rectangular waveform appearing at these continuous portions. The related device cannot, however, determine odd and even numbers of regenerated clocks from the extracted transition points. In this case, the transition points are not just boundaries of the bit periods. The related device therefore has to add special bit strings, from a few to several tens of bits to the data.
It is the object of the present invention to take into consideration the above problems and therefore to provide technology where it is no longer necessary to use a specific bit string in order to decide upon odd or even Manchester encoded data. To achieve this object, the present invention therefore provides technology in such a manner that a specific circuit does not have to be used in order to decide upon odd or even Manchester encoded data and provides technology capable of decoding Manchester encoded data to NRZ encoded data.
In order to resolve the aforementioned problems, in the present invention a method for decoding Manchester encoded data is provided with the following steps.
Extracting a clock component from input data inputted at a prescribed rate;
taking the extracted clock component as input and extracting transition points from the signal waveform of the clock component;
generating a clock signal of the same rate as the input data, that is in synchronism with the phase of the extracted transition points;
extracting a data component from the input data;
outputting results of comparing the extracted data component and a prescribed value as a binary level signal; and
outputting the binary level signal, taken in using the clock signal, as NRZ encoded data corresponding to the input data.
In order to resolve the aforementioned problems, in the present invention, a Manchester encoded data decoding device is provided with the following.
A Manchester encoded data decoding device comprising:
a first low pass filter for extracting a clock component from input data inputted at a prescribed rate;
a transition extractor for taking the extracted clock component as input and extracting transition points from the signal waveform of the clock component;
a clock generator for generating a clock signal of the 1 MHz, that is in synchronism with the phase of the extracted transition points;
a second low pass filter for extracting a data component from the input data;
an encoder for outputting results of comparing the extracted data component and a prescribed value as a binary level signal; and
a decoder for outputting the binary level signal, taken in using the clock signal, as NRZ encoded data corresponding to the input data.
Further, the filter output of the first low pass filter is the integrated waveform of the clock component. The transition points of the integrated waveform then appear in the vicinity of xc2xd time slots where the polarity of the Manchester code is inverted. The filter output of the second low pass filter is the integrated waveform for the data component. Information for the leading half portion of the time slot for the integrated waveform therefore appears as an extremely large value or an extremely small value in the vicinity of the xc2xd time slot where the polarity of the Manchester code is inverted.
The technology for the present invention takes out a binary level signal constituting the results of comparing a filter output of the second low pass filter occurring at timings of a regenerated clock signal and a prescribed value, using the regenerated clock signal. The technology of the present invention therefore reflects information for the leading half of the corresponding time slot and is capable of decoding Manchester encoded data to NRZ encoded data.